<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<div id="id1">
    <button v-on:click="reduce">-</button>
    {{num}}
    <input value="+"  type="button" @click="add1">
</div>
<script src="https://cdn.jsdelivr.net/npm/vue/dist/vue.js"></script>
<script>
    var app=new Vue({
        el:"#id1",
        data:{
            num:1
        },
        methods:{
          add1: function (){
              this.num++
          },
          reduce: function (){
              this.num--
          }
        }
    })
</script>
</body>
</html>